Adsorption Performance Of Heavy Metals In Sediments And Fluctuating Zone And Mechanisms

With the development of industry,manufacturing,agriculture and so on,in the production process of metallurgical,chemical,paper,pesticide,fertilizer and other fields will be accompanied by large-scale high concentrations of heavy metal pollution wastewater,only a small part of the plants have the ability to process wastewater to dischargeable level.The natural water such as rives and lakes,will be the main recipient parts of the untreated heavy metal waste water.So it has been a great ecological and environmental impact and damage to natural water body.In the past decade,heavy metal wastewater pollution incidents continue to increase.Study shows that when the heavy metal contaminants entering the water will be rapidly deposited in the sediments of the river and the soil of the fluctuating zone,and the content of heavy metals in the water is several orders of magnitude different from that of the heavy metals in the sediments.Therefore,study on the form of heavy metal existence and its adsorption mechanism in the sediments and fluctuating zone soil is very important.In this study,we focus on a secondary tributary of the Three Gorges Reservoir,near Chongqing main districts.In this research we analyze contents of elemental and background heavy metals in the sediments and soil and the adsorption kinetics and thermodynamics experiments of Ni,Hg and As.Based on the analysis,the main soil background elements in the sediments and the fluctuating zone soil are O,Si,C and Al.From the Fourier transform infrared spectroscopy analysis,it can be seen that the sediment and the fluctuating zone soil have similar chemical functional groups.According to the "soil environmental quality standards"(GB15618-1995),the heavy metal content of this secondary tributary is under natural background valueAccording to adsorption experiment,four common adsorption kinetic models have been taken to study.The result shows Elovich model has the best correlation coefficient,fowllwing by the pseudo-second order adsorption kinetic model and the pseudo-first order kinetic model,the int-diffusion model may not suitable for the adsorption of Ni and Hg.When the adsorption experiment goes about 40 min,the amount of adsorption has been saturated,after adsorption for 4h,adsorption capacity is almost no increase,the adsorption ends.When the adsorption is balanced,according to the pseudo-second order adsorption kinetic model the average adsorption capacity of Ni was 2.922mg/g and the average adsorption capacity of Hg was 1.768mg/g.From the results of adsorption experiments,the sediments and the fluctuating zone have little adsorption on As.In the experimental of thermodynamics adsorption,it is found that the adsorption of Ni is beneficial to the increase of temperature.The adsorption of Ni on the sediments and the the fluctuating zone is the endothermic process.The thermodynamic parameter calculation from Ni adsorption process results indicate that this process is spontaneous endothermic.But the temperature increases from 25 °C to 35 °C.The increase in the amount of adsorption is less than the increase in the adsorption capacity of the temperature from 15 °C to 25 °C.From the results of adsorption isothermal curve fitting,Langmuir adsorption isothermal equation can better describe the adsorption process of Ni than Freundlich adsorption isothermal equation.Hg is beneficial to the decrease of temperature.The adsorption of Hg on the sediments and the the fluctuating zone is the exothermic process.The thermodynamic parameter calculation from Hg adsorption process results indicate that this process is spontaneous.When the temperature decreases from 35 °C to 15 °C.there shows the increase of adsorption.From the results of adsorption isothermal curve fitting,Freundlich adsorption isothermal equation can better describe the adsorption process of Ni than Langmuir adsorption isothermal equation.FTIR spectra of before and after sediment and fluctuating zone soil adsorption of heavy metals show that the position of carboxylic acid(-COOH)functional absorption peak changes,presumably the carboxyl groups in the sediment and fluctuating zone soil contribute to the adsorption of Ni and Hg during the adsorption process.Further research by X ray photoelectron spectroscopy to study the bond form of heavy metals in sediment and fluctuating zone shows that Ni is mainly form Ni-O bond,Hg is also in formation of Hg-O,part of As is oxidized from +3 to +5 in when adsorbed by the sediment and fluctuating zone soil.The conclusion of XPS spectrum is consistent with the FTIR conclusion.